Recovery of tertiary base olefins



April 5, 1949.

R. A. FINDLAY RECOVERY OF TERTIARY BASE OLEFINS Filed June 21, 1946 N OILVNOI LOVER INVENTOR. R A FINDLAY SNIddIHLS CINV NOIJDVBU ATTORNEYS Patented Apr. 5, 1949 UNITED STATES of Delaware PATENT OFFICE Robert A. Findlay, Bartlesville, Okla., assignor to Phillips Petroleum Company, a corporation Application June 21, 1946, Serial No. 678,278

4 Claims.

This invention relates to the recovery of tertiary base aliphatic olefins from admixture with other hydrocarbons especially non-tertiary aliphatic olefins having the same number of carbon atoms per molecule. In one of its specific aspects the invention relates to the recovery of isobutylene from admixture with other aliphatic C4 hydrocarbons such as normal butylene, butanes, etc.

The tertiary base aliphatic olefins often occur in hydrocarbon mixtures containing other hydrocarbons usually having the same number of carbon atoms per molecule. It is often very difficult to effect a separation of the tertiary base olefin in concentrated or substantially pure form from such mixtures by conventional means such as fractional distillation. Use of the more recently developed methods such as extractive distillation, azeotropic distillation, etc., is often not feasible. Accordingly, a simple and economical method of recovering such tertiary base olefins in concentrated or substantially pure form would be of great value.

The principal object of the present invention is to provide a method of recovering tertiary base aliphatic olefins in concentrated or substantially pure form from hydrocarbon mixtures containing same. Another object is to provide a method of recovering such tertiary base olefins from mixtures containing same together with non-tertiary aliphatic olefins having the same number of carbon atoms per molecule. Another object is to provide an improved method of recovering isobutylene from admixture with normal butylene or butylenes. Another object is to provide an improved method of recovering tertiary base aliphatic olefins from the corresponding tertiary alkyl chlorides. Still another object is to provide an improved method of recovering isobutylene from tertiary butyl chloride. Numerous other objects of the present invention will be apparent to those skilled in the art from a consideration of the following detailed description.

The accompanying drawing portrays diagrammatically one form of equipment which may be used for recovering tertiary base aliphatic olefins from hydrocarbon mixtures containing same together with other hydrocarbons especially the corresponding non-tertiary olefins, in accordance with the present invention.

In one aspect the present invention is a process of recovering tertiary base aliphatic olefins from the corresponding tertiary alkyl chlorides which comprises heating the tertiary alkyl chloride in the presence of a high-boiling essentially paraffinic and/or naphthenic hydrocarbon oil to a temperature such that the tertiary alkyl chloride is decomposed to the tertiary base olefin and hydrogen chloride, causing the tertiary base olefin selectively to dissolve in the high-boiling oil immediately upon liberation of said olefin, withdrawing the liberated hydrogen chloride, sepa-v rately withdrawing the solution of the tertiary base olefin in the oil, and recovering the tertiary base olefin from solution in the oil in any suitable manner, usually by fractional distillation or stripping.

In a preferred embodiment of the present invention, a tertiary base aliphatic olefin is continuously recovered in substantially pure form from the corresponding tertiary alkyl chloride by continuously feeding a stream of the tertiary alkyl chloride at an elevated temperature and in admixture with a recycled oil stream hereinafter described into a vertical elongated decomposition tower, continuously feeding cooled essentially parafiinic and/ or naphthenic absorption oil composed of hydrocarbons having at least 10 carbon atoms per molecule into the top of the tower and causing the oil to descend therein, reboiling the material attaining the bottom of the tower and thereby maintaining a temperature of about 500 F. in the bottom of the tower, thereby decomposing the tertiary alkyl chloride into the tertiary base olefin and hydrogen chloride and absorbing the liberated tertiary base olefin selectively in the oil immediately upon its liberation, withdrawing the liberated hydrogen chloride as an overhead from the top of the tower, withdrawing the oil containing the dissolved tertiary base olefin from the bottom of the tower and fractionating same, usually by fractional distillation or stripping, to separate the dissolved tertiary base olefin overhead from the oil as bottoms product, cooling a minor portion of the oil thereby recovered and recycling the same to the top of the decomposition tower, and recycling the major portion of the oil withdrawn as bottoms product without cooling and admixing with the tertiary alkyl chloride stream entering the decomposition tower.

I have found that by decomposing the tertiary alkyl chloride in the reboiling section of the decomposition tower in the presence of a highboiling oil which is capable of dissolving the tertiary base olefin and incapable of dissolving the hydrogen chloride, the tertiary base olefin is recovered in a state of high purity, often substantially per cent. The conditions in the decomposition zone are such as to favor the removal of hydrogen chloride as fast as it is formed thereby resulting in more complete decomposition of the tertiary alkyl chloride and the recovery of the tertiary base olefin in a higher state of purity. The tertiary alkyl chloride and the tertiary base olefin are completely miscible with the absorption oil but the hydrogen chloride is substantially insoluble therein and therefore the products of the decomposition, namely the hydrogen chloride and the tertiary base olefin, are immediately upon their formation separated from one another thereby displacing the equilibrium in the desired direction.

The absorbent serves several purposes among which are the following: (1) it enables a high temperature and a low pressure to be obtained in the decomposition zone, both of these favoring decomposition; (2) it absorbs the tertiary base olefin which would otherwise leave the top of the decomposition column, while allowing the hydrogen chloride to be removed from the top of the column in the gaseous form; hence, if desired, the hydrogen chloride may be recycled to a preceding step hereinafter described in. which the tertiary base olefin in a hydrocarbon mixture is selectively reacted with hydrogen chloride to form the tertiary alkyl chloride fed to the decomposition step; (3) it dilutes the mixture thereby suppressing recombination of the tertiary base olefin and the hydrogen chloride once they are formed; and (4) it eliminates the need for refluxing the decomposing tower with hydrogen chloride which would require prohibitively high pressures and expensive refrigeration.

The decomposition tower is operated much like an absorber in that the absorption oil continuously descends therein countercurrently with respect to the hydrogen chloride. The decomposition tower is even more like an extractive distillation column in that the bottom of the tower is reboiled. However, this reboiling is primarily for the purpose of decomposition of the tertiary alkyl chloride and consequent generation of gaseous hydrogen chloride which is undissolved and passes up the column. Moreover the column is not refluxed by condensation of gaseous overhead as is customary in extractive distillation. Rather, reliance is placed upon continuous injection at the top of the column of sufficient cold absorption oil to keep the top temperature at the desired level and to insure proper column operation.

The absorption oil should be saturated, i. e., essentially paraflinic and/ or naphthenic, and should be sufiiciently high boiling that the dissolved tertiary base olefin can be readily separated therefrom as an overhead by ordinary stripping or fractional distillation. Preferably the initial boiling point of the absorption oil is at least 400 F. The absorber oil may advantageously consist essentially of paraffin and/ or naphthene hydrocarbons having 10 or more carbon atoms per molecule. These paraffin hydrocarbons may be straight chain or normal or they may be moderately branched. Examples of suitable absorption oils are high boiling kerosene, mineral seal oil, gas oil, paraffin oil, white mineral oil, normal dodecane, decalin, etc. 7

The amount of absorption oil present in the decomposition zone should be at least sufficient to dissolve all of the tertiary base olefin. Generally it is in considerable excess of this amount. It may range from to 20 times the amount required to dissolve all of the tertiary base olefin which could be liberated by decomposition of the tertiary alkyl chloride present. Since the process is generally practiced continuously with continuous introduction of both tertiary alkyl chlo- 4 ride and oil, the amount of oil will be determined by what is known as the oil rate.

The temperature at the top of the decomposition column is advantageously maintained below 130 F. Such temperatures may be obtained by the use of ordinary cooling water available at the refinery. The bottom temperature is preferably at least 500 F. and may range upwardly therefrom to a temperature at which reactions other than the desired decomposition to hydrogen chloride and tertiary base olefin take place. Usually the temperature at the bottom of the column will range from 500 to 600 F.

The pressure maintained on the decomposition column may range from atmospheric to moderately superatmospheric pressures. It is preferred to keep the pressure as near atmospheric as possible.

I generally apply my invention in such manner as to recover substantially pure tertiary base olefins from hydrocarbon streams containing same in admixture with other hydrocarbons having the same number of carbon atoms per molecule, especially the corresponding non tertiary olefins, namely, the secondary olefins which are characterized by the grouping R-CI-I=CH. The secondary olefins consist of two types, namely, the normal olefins which have a straight chain and the secondary iso olefins which have a The tertiary base olefins on the branched chain. other hand are characterized by the grouping Thus isobutylene is a tertiary base olefin whereas the normal butylenes are not. In the pentenes or amylenes, 2-methyl butene-l and 2-methyl butene-Z are the only tertiary base olefins. In

the hexenes the tertiary base olefins are 2,3-

dimethyl butene-l, Z-methyl pentene-l, 2-methyl pentene-Z, 3-methyl pentene-Z and 2-ethyl butene-l. The present invention is applicable to the recovery of any tertiary base olefin but is of greatest importance in the recovery of the tertiary base C4-C6 olefins.

As applied to the recovery of tertiary base olefins from hydrocarbon mixtures containing same in admixture with other hydrocarbons having the same number of carbon atoms per molecule, such as the corresponding non-tertiary olefins, the present invention may be a continuous process and may comprise continuously feeding the hydrocarbon mixture into the top of a vertical elon-- gated reaction-stripping zone and passing same downwardly therein, continuously feeding a stream of anhydrous hydrogen chloride into this zone at a point which may advantageously be substantially below the point of entry of the hydrocarbon feed so that countercurrent contact between the hydrocarbon feed and the hydrogen chloride is obtained, passing the resulting mixture into the lower or stripping portion of the zone, causing selective reaction of the tertiary base olefin with the hydrogen chloride in the reaction-stripping zone to form the tertiary alkyl chloride, reboiling the mixture in the bottom of the zone and thereby stripping out unreacted hydrogen chloride but not to any appreciable ex tent decomposing the tertiary alkyl chloride, withdrawing from the top of the zone overhead vapors containing anhydrous hydrogen chloride which is recycled to the zone, withdrawing from the zone a bottoms product consisting essentially of the tertiary alkyl chloride and the unreacted hydrocarbons derived from the original feed, fractionally distilling this bottoms product in a separate fractionation zone to separate the unreacted hydrocarbons as an overhead from the tertiary alkyl chloride as a kettle product. This tertiary alkyl chloride is then fed into the decomposition process described above.

An excess of hydro-gen chloride is maintained in the reaction zone to insure conversion or" all the tertiary base olefin in the feed to the tertiary alkyl chloride.

The hydrogen chloride is generally introduced in gaseous form to the reaction-stripping zone; however liquid hydrogen chloride may be emloyed if desired. Gaseous hydrogen chloride serves as well as liquid hydrogen chloride and may be used at lower pressures for the same tem perature, and furthermore mechanical problems such as plugging may be less with the anhydrous hydrogen chloride gas.

The temperature in the top of the fractionation tower wherein the unreacted hydrocarbons are separated from the tertiary alkyl chloride is preferably maintained at not above 123 F. in order to effect recombination of any hydrogen chloride and tertiary base olefin formed by any decomposition which may take place in the bottom of this fractional distillation column.

The conditions in the reaction-stripping col umn should be such as to favor reaction of hydrogen chloride with tertiary base olefins. High pressures and relatively low temperatures favor this reaction. Pressure may range from atmospheric up to several hundred pounds per square inch absolute say 500 pounds. The temperature and pressure are correlated to obtain the desired result. The temperature in the bottom of the column is preferably not over 200 F. and may conveniently range from 100 to 200 F. The top temperature may range downwardly to as low as l00 F. but temperatures below 0 F. may not be feasible because of the expense of the refrigeration required. The top temperature and the pressure are correlated so that the overhead product comprises gaseous hydrogen chloride together with volatilized hydrocarbons other than the tertiary olefin content of the feed. overhead product is ordinarily recycled in the gaseous state but it may be condensed prior to such recycle.

The conditions of temperature and pressure maintained in the fractional distillation zone which the unreacted hydrocarbons are separated from the tertiary alky1 chloride should be such that this separation is accomplished without substantial formation of hydrogen chloride and tertiary base olefin. This may be accompli holding the top temperature at not over 100 F. in order to effect the recombination of any hydrogen chloride and tertiary base olefin which may have been formed by decomposition in the bottom. This column may be operated with a bottom temperature ranging up to 200 If superatmospheric pressure is employed. the bottom temperature may be higher without causing objectionable decomposition of the tertiary allzyl chloride.

I prefer to condense the hydrogen chloride removed as an overhead from the top of the decomposition tower and to recycle the resulting liquid hydrogen chloride to the reaction-stripping zone.

If the reaction-stripping tower and the in which the unreacted hydrocarbons are rated from the tertiary alkyl chloride are tower sepaoperated at high pressure, it will be necessary to use suitable pressure reducing means on the stream of tertiary alkyl chloride fed from the fractionator where the unreacted hydrocarbons are removed to the decomposition column.

The tertiary alkyl chloride stream prepared in the reaction-stripping column and the subsequent fractionator is substantially pure so that contamination of the materials in the decomposition and subsequent fractionation is avoided.

"Water is rigorously excluded from the entire system primarily since it would cause excessive corrosion. If anhydrous conditions are maintained throughout no serious corrosion problem is encountered.

In the drawing, a hydrocarbon feed containing isobutylene or other tertiary base aliphatic olefin such as a tertiary base pentene or pentenes (2- methyl butene-l and/or 2-methy1 butene-Z) or a tertiary base hexen or hexenes (e. g. Z-methyl pentene-l, Z-methyl pentene-Z, 3-methyl pentene-Z, Z-ethyl butene-l or 2,3-dimethylbutene-1, either singly or in admixture) enters the system via line i and is fed continuously into the top of reaction-stripping tower 2. The feed then descen past the point at which hydrogen chloride ente the tower via line 3. Reaction between the tertiary base olefin and the hydrogen chloride takes place as the feed flows downwardly. The lower portion of tower 2 is a stripping section and as the reaction mixture fiows therethrough the unrca-cted hydrogen chloride is removed. The excess hydrogen chloride leaves the top of the tower via line l. The hydrogen chloride so withdrawn is recycled via line 6 together with hydrogen chloride liberated by decomposition at a later point in the system. Make-up hydrogen chloride is introduced as needed via line I.

The bottom of tower 2 is reboiled to supply the heat necessary for stripping, as indicated by reboiler 8.

Hydrogen chloride-free hydrocarbons containing the tertiary alkyl halide (e. g. tertiary butyl chloride in the case of an isobutylene-containing feed) are passed continuously via line 9 to a fractionation column 59 where unreacted hydrocarbon is removed overhead, tertiary butyl chloride being removed at the bottom. The unreacted hydrocarbon removed overhead is withdrawn via line ll while the tertiary butyl chloride is withdrawn via line I2.

The top trays of column iii are kept close to atmospheric temperature, recombining any hydrogen chloride and isobutylene which may be formed by decomposition at the bottom of column H3.

The tertiary butyl chloride is then fed continuously through a heater it into a decomposition tower Hi, entering at an intermediate plate. An absorbent such as suitable oil is fed continuously into column M via line I5. The bottom of column is maintained at an elevated temperature (e. g. 500 P.) such as to effect decomposition of the tertiary butyl chloride into hydrogen chloride and isobutylene. This is accomplished by reboiling of the bottoms product by means of heater Hi. The hydrogen chloride leaves the top of column it. via line I! and is recycled to reaction zone 2 via lines 5 and 3.

A mixture of the absorbent and isobutylene leaves the bottom of column 1 via line l8 and passes to a fractionator 59 where pure isobutylene is recovered overhead and withdrawn vi-a line 20 as the product of the process. The absorbent is recovered as bottoms product Withdrawn via line if. A major portion of the hot absorbent is recycled via line 22 and combined with the tertiary butyl chloride entering decomposition tower l4. A minor portion of the absorbent is passed via line 23 through cooler 24 and used as reflux for tower [4.

Fresh oil, as required for make-up is introduced via line 25.

As mentioned above, if columns 2 and I0 are operated at high pressure, it will be necessary to interpose suitable pressure reducing means in line l2 to lower the pressure on the tertiary alkyl chloride stream to the pressure maintained in decomposition tower It. This is indicated by optional line 26 containing pressure reducing valve 27.

From the foregoing many advantages of my invention will be apparent to those skilled in the art. The principal advantage is that the decomposition of the tertiary alkyl chloride is conducted in such a manner that the decomposition products are immediately separated from one another, the tertiary base olefin going into solu-' tion in the oil and the hydrogen chloride being liberated in the gaseous phase. Another advantage is that a simple and effective method of separating tertiary base olefins from corresponding hydrocarbons especially corresponding non-tertiary olefins is provided. Many other advantages of the process of my invention will be recognized by those skilled in the art.

I claim: l

l. The continuous process of recovering substantially pure low-boiling tertiary base olefin from a tertiary alkyl chloride bontaining from 4 to 6 carbon atoms per molecule which comprises continuously feeding said tertiary alkyl chloride at an elevated temperature and in admixture with a hot recycled absorption oil stream hereinafter described and consisting essentially of saturated hydrocarbons having at least 10 carbon atoms per molecule into a vertical decomposition zone at a point therein intermediate the top and bottom thereof, continuously feeding cooled recycled absorption oil consisting essentially of saturated hydrocarbons having at least 10 carbon atoms per molecule into the top of said zone at a temperature below 180 1' and causin same to descend therein, reboiling the material attaining the bottom of said zone and maintaining a temperature of at least 500 F. in the bottom of said zone, thereby decomposing said tertiary alkyl chloride and absorbing the liberated corresponding tertiary base olefin selectively in said oil immediately upon liberation thereof, withdrawing liberated hydrogen chloride as an overhead from the top of said zone, withdrawing the hot oil containing the dissolved tertiary base olefin from the bottom of said zone and passing same Without cooling to a fractionating zone and therein separating said tertiary base olefin as an overhead product from said hot oil as bottoms product, cooling a minor portion of said hot oil to a temperature below 130 F. and recycling same to the top of said decomposition zone as aforesaid, and recycling the major portion of said hot oil Without cooling and admixing same with the tertiary alkyl chloride fed into said decomposition zone.

2. The continuous process of recovering substantially pure isobutylene from tertiary butyl chloride which comprises continuously feeding said tertiary butyl chloride at an elevated temperature and in admixture with a hot recycled absorption oil stream hereinafter described and consisting essentially of saturated. hydrocarbons having at least 10 carbon atoms per molecule into a vertical decomposition zone at a point therein intermediate the top and bottom thereof, continuously feeding cooled recycled absorption oil consisting essentially of saturated hydrocarbons having at least 10 carbon atoms per molecule into the top of said zone and causing same to descend therein, reboiling the material attaining the bottom of said zone and maintaining a temperature of at least 500 F. in the bottom of said zone, thereby decomposin said tertiary butyl chloride and absorbing the liberated isobutylene selectively in said oil immediately upon liberation thereof, withdrawing the liberated hydrogen chloride as an overhead from the top of said zone, Withdrawing the hot oil containing the dissolved isobutylene from the bottom of said zone and passing same without cooling to a fractionating zone and therein separating isobutylene as an overhead product from said hot oil as bottoms product, cooling a minor portion of said hot oil to a temperature below 130 F. and recycling same to the top of said decomposition zone as aforesaid, and recycling the major portion of said hot oil without cooling and admixing same with the tertiary butyl chloride fed into said decomposition zone.

3. The continuous process of recovering substantially pure low-boiling tertiary base olefin from a tertiary alkyl chloride containing from 4 to 6 carbon atoms per molecule, which comprises continuously feeding said tertiary alkyl chloride at an elevated temperature and in admixture with a hot recycled absorption oil stream hereinafter described having an initial boiling point of at least 400 F. into a vertical decomposition zone at a point therein intermediate the top and bottom thereof, utilizin 5 to 20 times the amount of absorption oil required to dissolve the tertiary base olefin hereinafter produced, continuously feeding cooled recycled absorption oil consisting essentially of saturated hydrocarbons having at least 10 carbon atoms per molecule into the top of said zone at a temperature below 130 F. and causing same to descend therein, reboiling the material attaining the bottom of said zone, thereby decomposing said tertiary alkyl chloride and absorbing the liberated corresponding tertiary base olefin selectively in said oil immediately upon liberation thereof, withdrawing liberated hydrogen chloride in vapor phase as an overhead from the top of said zone, withdrawing the hot oil containing the dissolved tertiary base olefin from the bottom of said zone and passing same without cooling to a fractionating zone and therein separating said tertiary base olefin as an overhead product from said hot oil as bottoms product, cooling a minor portion of said hot oil to a temperature below 130 F. and recycling same to the top of said decomposition zone as aforesaid, and. recycling the major portion of said hot oil Without coolin and admixing same with the tertiary alkyl chloride fed into said decomposition zone.

4. The continuous process of recovering substantially pure low-boiling tertiary base olefin from a tertiary alkyl chloride containing 4 to 6 carbon atoms per molecule which comprises continuously feeding said tertiary alkyl chloride at an elevated temperature and in admixture with a hot recycled absorption oil stream hereinafter described having an initial boiling point of at least 400 F. into a vertical decomposition zone at a point therein intermediate the top and bottom thereof, utilizing 5 to 20 times the amount of absorption oil required to dissolve the tertiary base olefin hereinafter produced, continuously feeding cooled recycled absorption oil consisting essentially of saturated hydrocarbons having at least 10 carbon atoms per molecule into the top of said zone at a temperature below 130 F. and causing same to descend therein, reboiling the material attaining the bottom of said zone and maintaining a temperature in the range of 500 to 600 F. in the bottom of said zone, thereby decomposing said tertiary alkyl chloride and absorbing the liberated corresponding tertiary base olefin selectively in said oil immediately upon liberation thereof, withdrawing liberated hydrogen chloride in the vapor phase as an overhead from the top of said zone, withdrawing the hot oil containing the dissolved tertiary base olefin from the bottom of said zone and passing the same without cooling to a fractionating zone and therein separating said tertiary base olefin as an overhead product from said hot oil as bottoms product, cooling a minor portion of said hot oil ROBERT A. FINDLAY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,087,961 Masland Feb. 24, 1914 1,384,447 Gardner et a1 July 12, 1921 2,156,070 Stern et a1 Apr. 25, 1939 2,181,642 McMillan Nov. 28, 1939 2,368,446 Buc Jan. 30, 1945 

